I took the index in the words, transformed the range to binary, included three zeros, calculated the sha256 digest, took the 1st part of the hexadecimal to convert it to binary, included three zeros to your eight digits of your binary and acquired 00000010011 which translates to 19 in decimal. https://bookmarkingbay.com/story19022601/a-review-of-bip39-phrase-list